This invention relates to a method and apparatus for traversing a strand or strands to form a restrained cross-laid web. More particularly, it relates to a method adaptable to forming restrained webs of a wide variety of strand laydown patterns, and to apparatus upon which the method can be carried out at high speed.
A "restrained web" is one in which the strands which comprise the web, after being cross-laid in a given configuration, are held in that configuration by pins or other restraining elements until a desired operation is carried out upon the web. Additional tension may be applied to the restrained web by increasing the distance of the pins across the web after it is laid.
Many types of machines have been developed for withdrawing a strand from a package and traversing it across a moving conveyor to form a web useful for reinforcing paper or other sheet materials, of for forming scrim or other fabrics. The cross-laid web is frequently combined with a warp sheet of strands, and the two sheets may be bonded together with adhesives or otherwise. However, most of the prior art apparatus can be operated only at relatively low speed. Many of these machines are restricted to laydown of a single strand, and others are incapable of forming a restrained web. Most of the prior art machines are restricted to a particular laydown pattern, e.g., a diagonal pattern, which can be varied only to a minor extent such as by changing the spacing of the strands. In particular, the achievement of a truly orthogonal laydown has been a problem in the prior art. This is important, since for many products it is desired to have reinforcing strands across the width of the product at right angles to the long or machine direction of the product.
Though the term "strand" will be used throughout the specification, this term is meant to include materials such as yarn, threads, cords, filaments and the like. Such strands may be of either natural or synthetic material.